An ultrasound study of frequency and co-articulation

Anticipatory coarticulation has been reported to be affected by word form frequency. However, it remains unclear whether frequency effect also modulates carry-over (perseverative) coarticulation. To investigate the interaction of word form frequency effect and carry-over/anticipatory coarticulations, ultrasound imaging was performed on the articulation of the vowel [a:] in German verbs. Effects of coarticulation were induced by controlling the verb’s suffixes and preceding pronouns. Contrary to the standard tongue contour analysis, we analyzed whole ultrasound images using Generalized Additive Models. We found more fronted tongue root, lower tongue body, and higher tongue tip in low-frequency words. By contrast, high-frequency words showed a more rounded tongue shape. This was reflected by the middle part of the tongue to be higher and the tongue root more retracted in high frequency words in comparison to low frequency words. These findings indicate more optimized tongue movements for higher frequency words.